X.25 is a protocol standard for Wide Area Network (WAN) communications that defines how connections between users devices and network devices are established and maintained. RBP is a protocol over TCP/IP that allows delimiting logical record boundaries and adds support for conveying logical records between a TCP/IP host using this protocol and an X.25 host using the X.25 M-bit (the “more data” flag in a X.25 data packet) to mark record boundaries. In other words, RBP protocol defines a way for hosts using TCP/IP based protocols to exchange data with devices that use X.25 protocol while preserving the logical record boundaries conveyed by the X.25 M-bit. RBP protocol translates data conveyed over a TCP session into one or more RBP packets, hence the TCP/IP packets, by appending a 6-byte RBP header to the data portion of each TCP/IP packet that specifies the amount of data following and indicates whether data in this packet is considered the final part of a logical record. The 6-byte RBP header is located at the start of the data portion of a TCP/IP packet.
RBP protocol was developed to enable the Telco Data Communication Network (DCN) Service Provider customers to migrate from the legacy X.25 DCNs to IP-based DCNs while maintaining the legacy X.25 equipment at one end. The original RBP protocol does not support conveyance of Q-bit data packets between X.25 and TCP/IP hosts. Q-bit data packets are packets with the “qualified” bit set to indicate that the packets carry control information rather than user data. Receipt of a X.25 Q-bit data packet terminates the corresponding X.25 and TCP connections in the original RBP implementation.